The myxobacteria are a group of Gram-negative bacteria that exhibit multicellular behavior and can undergo primitive differentiation. They provide a useful system for studying cell-cell interaction and development in a simple organism because they resemble more familiar Gram-negative bacteria in their structure and they can be grown and manipulated with ease. Myxobacteria can grow vegetatively like other bacteria but, when nutrients become limiting, myxobacteria aggregate to form fruiting bodies. Within the fruiting bodies, the cells sporulate, changing from the long vegetative rods to short ovoid spores with refractory properties. Under appropriate conditions, the spores germinate to give vegetative cells once more. Our objectives are to identify the signals that myxobacteria exchange when they interact with each other to form fruiting bodies.